This invention relates to devices for transferring persons or material between a stationary object, such as an offshore platform, and a moving object, such as a ship.
Oil rigs and drilling platforms are serviced by the regular transfer of operating personnel from supply vessels to the platforms, and vice versa, in virtually all weather conditions. Typical marine transfer devices utilize a crane or service derrick that is mounted to the offshore platform to lower a gangway or ramp to an adjacently moored ship.
When transferring personnel or material between the platform and the ship, the safety and efficiency of the operation can be greatly hampered by adverse weather or sea conditions. A common problem encountered with prior art transfer devices is easily and securely coupling the device to a ship that may be rolling, pitching or surging in response to wave action at the platform site. Further, when a prior art device is connected, the motion of the ship usually is transmitted to the transfer device, making negotiation difficult and potentially hazardous.
The use of current marine transfer devices most generally is restricted to vessels that have undergone the modifications necessary for connection with the transfer device. These modifications typically include reinforcing the ship's structure and attaching a receptacle to the ship's deck for receiving the outboard end of the device.
Pitts et al., U.S. Pat. No. 2,641,785, which is typical of prior proposals for marine transfer devices, discloses a marine transfer ramp, the operation of which involves directing a ball point on the end of the ramp into a cup that is attached to the deck of the ship. Although this arrangement may be satisfactory under some conditions, effecting this type of connection under conditions where the ship is thrashing about its moorings can be difficult and time-consuming.
Ryan, U.S. Pat. No. 4,003,473, which also illustrates the prior art, discloses a combined marine ramp transfer and mooring system that is connected to the ship by threading a hang line (which is attached to the ramp) through a docking pedestal that is mounted to the ship's deck. The end of the ramp is then drawn toward the pedestal so that a ramp attacher assembly can be latched thereto. Ryan's system is designed so that the ships rolling motion is transmitted to the ramp, resulting in twisting movement of the ramp. Ryan also calls for reinforcing the ship's structure in order to accommodate the forces that are placed on the docking pedestal.